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Vibrio parahaemolyticus is responsible for seafood-borne gastroenteritis worldwide. Isolates of V. parahaemolyticus from clinical samples (n=74) and cockles (Anadara granosa) (n=74) in Thailand were analyzed by serotyping, determination of virulence and related marker genes present, response to antimicrobial agents, and genetic relatedness. Serological analysis revealed 31 different serotypes, 10 of which occurred among both clinical and cockle samples. The clinical isolates commonly included the pandemic serogroup O3:K6, while a few of the cockle isolates exhibited likely pandemic serovariants such as O3:KUT and O4:KUT, but not O3:K6. The pandemic (orf8 gene-positive) strains were more frequently found among clinical isolates (78.4%) than cockle isolates (28.4%) (p<0.001). Likewise, the virulence and related marker genes were more commonly detected among clinical than cockle isolates; i.e., tdh gene (93.2% versus 29.7%), vcrD2 (97.3% versus 23.0%), vopB2 (89.2% versus 13.5%), vopT (98.6% versus 36.5%) (all p<0.001) and trh (10.8% versus 1.4%) (p<0.05). Pulsed-field gel electrophoresis of NotI-digested genomic DNA of 41 randomly selected V. parahaemolyticus isolates representing different serotypes produced 33 pulsotypes that formed 5 different clusters (clonal complexes) (A-E) in a dendrogram. Vibrio parahaemolyticus O3:K6 and likely related pandemic serotypes were especially common among the numerous clinical isolates in cluster C, suggesting a close clonal link among many of these isolates. Most clinical and cockle isolates were resistant to ampicillin. This study indicates that O3:K6 and its likely serovariants based on the PFGE clusters, are causative agents. Seafoods such as cockles potentially serve as a source of virulent V. parahaemolyticus, but further work is required to identify possible additional sources., (Copyright © 2016. Published by Elsevier B.V.)

Vibrio vulnificus can cause septicemia, wound infection and gastroenteritis. The most severe infections are related to consumption of raw or undercooked seafood. Virulence genes, biomarkers, antimicrobial resistance, and genetic relationships among V vulnificus isolated from clinical and environmental sources in Thailand have not hitherto been investigated. ViuB encoding vulnibactin siderophore was detected in 33% and 50% of clinical and environmental (cockle) V. vulnificus isolates, respectively, and capsular polysaccharide allele 1 in 67% and 75% of clinical and environmental isolates, respectively. Analysis of the 16 S rDNA gene revealed that type B was the most frequent in both clinical and environmental isolates (67%) whereas the non type-able (30%) was detected only in environmental isolates. The virulence-correlated gene (vcg) with both type C and E together was the most frequently found among the clinical (67%) and environmental (72%) isolates. Pulsed-field gel electrophoresis differentiated V vulnificus into 2 clusters; most cockle samples (83%) and all clinical isolates grouped into cluster II, indicating a possible clonal relationship between V. vulnificus isolated from patients and cockles. Only 20% of environmental isolates were resistant to ampicillin. These studies suggest that V vulnificus isolated from cockles has virulence genes similar to those in clinical isolates and thus may have the potential of causing disease.